Monopack film sensitized with layers containing different silver halides



Feb. 1l, 1941. l K scHlNzEL 2,231,684

YuonoPMJi FLL! sENsITIzED WITH LAYERS CONTAINING DIFFERENT SILVER HALIDES Original Filed April 29, 1937 TN/YED.

JE/YS/T/VE .SILVER CHLOE/0E.

YELLW RED ORANGE ITM/E, S/L VER BROMIDE.

REo 0R 6REEN-YELL0W :ENS/77 YE,

`s/L YER ERoM/DE.

25 F/6.6 Y 4 UE SENS/NVE /S/L VER CHLOR/DE). '275 f sE/vs/T/YE.

/ /f//f/rf//f//l/ 7`. 2 YELLOW-GREEN E/YS/T/VE.

245 ggg CHL aR/DE, EL UE sE/Ys/T/VE. 27C y ,f, ,ff f/,f/ 4, LVER ROM/0E. s v oo/N LAYER, RED EENS/Tl VE. 26C YE LAYER.

1N ENToR KARL JcfIg/.NZEL l E? 6?. EMM

ATTORNEYS fPaiented Feb. 1 1, 1941 I MONOPACK FILM SENSITIZED WITH LAY- ERS (NTAINING DIFFERENT SILVER j.: :ll

Karl Schinzel, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation oi New Jersey l Original application April 29, 1937, Serial No.

139,759. Divided and this application August 9, 1938, Serial No, 223,946

5 claims, (ci. as-ei tance from eachother during the chemical ren This invention relates to color photography and particularly to processes of the type known as monopack, that is, involving the use of differentially color sensitive layers permanently superposed on a single support. This application is a division of my prior application Serial No. 139,- 759 iiled April 29, 1937. y

In the present invention the residual developable silver halide or that formed on. the original latent image by general rehalogenation or re` halogenation of each layer is immediately developed to the corresponding nal part image, unless other coloring methods are applied for one of the layers. Progress has been made by the present invention since by it differential diusion of reagents into the layers is rendered unnecessary and the process is, therefore, free from the uncertainties of penetration and since production oi entirely or `almost true color photographs optically has been made possible without uncertainty and complicated developing machines, and this with the purest vat dyes.

Reference will bef-*made from time to time, throughout this? speciilcation to the accompanying drawing which shows enlarged sections of photographic illm embodying certain of my inventions or useful in my improved processes andv in which the same reference characters indicate the same elements.

Figs. l, 2 and 3 show sections oi'. nlm having three differentially' lcolor sensitized layers on one side of the support, the several iigures illustrating different embodiments.

Fig. 4 shows in section an embodiment of lm in which a single layer of emulsion is diierentially color sensitized in diierent zones, in connection with other color sensitized layers.

Figs. 5, 6 and 7 show in section diilerent embodiments having differentially color sensitized layers on the opposite surfaces.,

The three-layer. material Referring to Fig. l, the support S carries the differentially sensitized layers l, 2 and i, the

upper layer i is generally blue-sensitive, the middle layer 2. yellow and green sensitive and the lower layer 3 red sensitive. In order to limit diffusion to a minimum, it is advisable to make the two upper layers asl thin as possible, about 0.005-0,01 mm., requiring the use of very linegrain emulsions, relatively poor in silver, for three-,color reversal development. In case lter layers and E are interposed, strongly swelling gelatine may be used for these. so that the'indlvidual layers are separated by the proper disactions. These lter layers are kept so thin, 0.01 mm. or less, that harmful diluslon is not increased, even ii?4 they should swell. to ten timesl their size. The lower layer can have the normal thickness oi. 0.02 mm.,forrevers al development 0.01-0.015 mm., so that the total thickness of the three layers is 0.025,-0240 mm. While the two upper layers require developers which deposit .especially productive and intensive dyes on the image, less intensity is required for the lower layer, since this layer may contain considerably more silver halide than the upper and also middlelayers. A similar intensity balance of the separation images is often obtained by addition of sulfte to the reversal developer for the lower layer, while this is omitted for the other layers.

In order to obtain a vigorous, well-graded blue image,\which is of primary importance for the character of the color photograph, coating of the lower red-sensitive emulsion (for printing, also infrared-sensitive) of an average thickness oi about 0.02 mm';v` using a highly sensitive emulsion of medium soft gradation, preferably sensitized only for red and orange, is recommended. Above this. a yellow and green-sensitive` emulsion -of medium sensitivity and a thickness of not more than 0.01 mm. is coated and over that a sensi-v tized emulsion of also medium sensitivity and not color sensitive and athickness oi. 0.005-0.01 mm.

For this purpose, transparent, coarse-grain silver y bromide emulsion can be used. Finest grain emulsions are, however, to be preferred, because their blue and blue-green sensitivity has been strongly increased by recent sensitizezs so that the speed of all layers is of the same order.

The efficiency of these sensitizers can be materially increased by ultrasensitization and hype'rsensitizatiom or according to the British Patent 385,545, and this is especially important if in the upper layer a pure silver chloride-or silver chloro-bromide gelatine emulsion is used, capable of being sensitized by thesensitizer of the British Patent 376,746 to ten times normal, and by ultrasensitization to 50 times normal, not much less 45 by pinaiiavol. If the finest-grain silver chloride emulsion is arranged in the middle, its sensitivity for yellow-green is already suiliciently high with the usual sensitizers, just as with silver bromide, and this is strongest if some ammonia or also soluble silver salts are added to the emulsion, as has 4been proposed for hyperand ultra-sensitization. 'Ihis increase in sensitivity vis sumcient for exposures, if modern 'high-aperture optics are used. l

The classical succession of the three layers can by having the upper emulsion sensitive to blueviolet, the middle emulsion to red and orange (or infrared) and the lower emulsion to yellow and green; in which case they are developed lemonyellow, green-blue and purple respectively. It is less desirable to arrange the layers so that the upper emulsion is redsensitive, the middle emulsion yellow-green sensitive and the lower emulsion blue sensitive, even if red sensitizers are produced today which in stronger concentration sensitize better for red than for 'blue (and this eiect can still be increased by adding desensitizers for blue).

Two-zone double layers Instead of obtaining differentially color sensitized strata by coating successive layers upon a common support, a somewhat similar resultant effect may be obtained by superncially treating a single previously sensitized layer so that it will, throughout a portion or zone have a sensitivity different from the remaining zone.

On Fig. 4 is shown a form in which an emulsion layer HD sensitized by erythrosin, rhodamine B, certain thio-pseudo-cyanines etc. is coated. on a non-color-sensitized silver halide gelatineor collodion-emulsion layer I3D. A yellow filter 12D may be arranged between them or the lower layer itself may be colored yellow. The extreme portion MD of the upper layer is then also sensialso for yellow-green.

tized for 'red with pinacyanol in dilute-alcoholic solution or with another sensitizer which under the proper conditions acts only superiicially. The results are, of course, only approximate, be cause the upper layer IID is sensitive throughout It is, therefore, recommended to eliminate a part of the yellow-green sensitizer by supercial action of alcohol or acetone. and to then sensitize for red. Orange-red coloring of this layer acts also in that respect since in the superficial treated portion principally only the red, and towards the middlew only the yellow-green rays, act during exposure through the back.

The upper or lower layer in any of thesev two zone double-layer forms may consist of silver chloride. Referring specifcallyto Fig. v4 a thin silver chloride gelatineor collodion-emulsion i3D of normal or reduced silver content, highly sensitized for blue or blue and green with dyes, and preferably containing an easily decolorized yellow filter dye. is first coated on the film. This is followed by a silver bromide gelatine emulsion of normal or reduced thickness, containing erythrosin or other yellow-green sensitizers in the emulsion. Then it is best to allow a dilute alcoholic solution of pinacyanol or other high-colloidal red sensitizers to act on this layer, preferably after drying. This sensitizes the extreme outer portion of this layer also for red.v

A pure alcoholic solution lof pinacyanol etc. or

' one diluted with lil-30% of water can also be allowed to act on the dry layer; or the swelled or hardened layer is sensitized with a pure alcoholic solution superficially applied with brushes, rollers or sprays. Exposure is made through the support.

Coating of both sides of the film 75 zone-double layers, the blue-sensitive layer may be in front and the layer which is sensitive to red and yellow-green by zones on the back side of the film. In these films coated on both sides, the support may be very thin, if the motion picture camera is of the continuous moving film type and development is done under such conditions which prevent strong swelling of the preferably moderately tanned gelatine layers. This is attained by addition of alcohol or salts preventing swelling, such as sodium carbonate, sodium sulfate etc. to the different baths, also by the use of developers containing much alcohol, if the dye generated is insoluble in it. In the three-layer plate, the lower layer, and in films coated on both sides, the middle'layer, can consist of silver halide collodium emulsion or an emulsion of silver halide in any other nonaqueous vehicle. In layers coated on different sides of the film, some may consist of silver halide collodion emulsion. In order to keep the pores of the collodion layer 26C open, a protective layer 6C, which may be of gelatine, dextrine, gum arabic etc. is coated over it serving at the same time as suppression or anti-halation protection. Thin films of cellulose acetate, Cello- .phane or synthetic colloids, lacquered on both Three-color reversal development After exposure or printing exposure, the superimposed latent images are developed to the three black separation silver images by an ordinary, non-tanning. preferably neutral developer, as ferrous oxalate, amidol, diamido-o-cresol etc. Most other organic developers in solutions containing sodiumcarbonate are also suitable, since they do not noticeably harm the color sensitivity, and this can be at least partially restored by the proper reagents. There is no emulsion for which the use of the so-called compensation developers for correction of the almost unavoidable differences in exposure of the individual separation emulsion is more recommended than for the triple layer.

In order to avoid the undesirable effect of local underexposure in the lower layers, it is best to bathe vall three layers first in a solution of the non-acting developer substance of a considerably stronger concentration than usual, and then to develop in solutions ofsodium carbonate, ammonia or weak alkalies. Simple concentrated developing solutions can be allowed to Adiiiuse with as low temprature as permissible and the development process started or accelerated by warming to room temperature or above. The

l same holds true for other reversal solutions.

Further treatment may be carried out in'difand depends upon whether lter ferent ways the sensitization is oxidaiayers are provided. or

tionstable or only developer-stable, or whether the upper layer consists of silver chloride etc. The greatest difllculty is to make the residual lsilver halide of the middle layer developable without influencing the other two existing part images.

, Usually, such sensitizers are selected, and this is assumed in the following examples, as are stable. at least to a neutral black developer and to the first weakly alkaline color developer. A special advantage of the invention, however, is the fact thatsensitization does not even have to withstand the ordinary general development, if the middle layer is surrounded by. two lters which are empenetrable to blue or ultra-violet light which latter makes the residual silver halide of the upper and middle layer developable, while the production of the middle part image is done, even without the action oi' light, by,- chemical pre-treatment with weak reducing agents or with the use of energetically. acting color developers. It is, of course, assumed that Yboth filter dyes are stable to the developer and are destroyed only later by acids, bases, oxidation or reduction. The lost color sensitivity can be restored by resensitization which, however, complicates the process.

It must not be omitted to mention that the character of the reversal images can befchanged to a certain degree by a very careful general exposure or additional exposure through color lters of all or some of the layers.

application of the principles of three-color reversal development as explained in thepreceding paragraphs, reference being made particularly to Fig. 1 by way. of example.

In the absence of lter layers and with sensi.- tization of the lower layer 3 exclusively for red or also orange or infrared, the initially reduced silver could be, as also in other cases, converted into silver ferrocyanide which is no moreldevelopable or only extremely slowly so with suitable color developers, or into highly dispersed silver iodide, or intoany other colorless silver salts which is insoluble, and diiiicultly reduced, preferably soluble inhypo, and decomposed by alkali or acid or. the metallic silver can be completely dissolved by oxidizing agents and washed out. Here and in analogous cases discussed later it is suflicient, if at least the highly dispersed silver of the upper layer I and, totally or partially also the fine-grain silver of the middle layer 2 is converted'in this manner. Waiting is then not necessary, (and this is a characterizing point of the present invention) until also the coarser negative silver of the lower layer 3 is converted or dissolved, since exposure of the residual silver halide of the middle layer 2 is best done from above. The residual silver halide of the middle layer 2 is then exposed to yellow or green light from either side and developed purple. vAfterQ this, the silver halide of the lower layer 3- is exposed to red light through the support S and developed green-blue. Finally, the residual silver halide of the upper layer I is exposed to blue or ultra-violet light and developed yellow. A variy ant of this procedure would be to re-ex'pose the lower layer 3 first to red light and develop green-,- blue, then re-expose the middle layer to yellow light from above, etc. In all these variants it is assumed that the sensitizers of the middle and lower layers are stable to mild oxidizing agents acting on metallic silver. lThis condition can best be fulfilled by the presence of highly dispersed silver, as it exists inthe highlysensitized grainless or very ne-grain silver halide emulsions of the upper or also middle layer. `,The color sensitivity can, however, be partially restored by dilute solutions of suliite, bisulte, hydrazine sulfate etc., unless addition of these agents with bleaching of the dye already formed does not take place.

The lower layer 3 can also be exposed to red light directly after primary general development and its residual silver halide developed greenblue, and only then all silver which was previously The following examples illustrate the practical dye, seleno indigo etc.) is .easily 3 reduced, or at least the highly dispersed silver of the upperlayer (or partially, also, the fine-A grain silverA of the middle layer), removed or preferably converted into silver ferrocyanide or the compounds mentioned above. The middle layer alone 2 is then exposed to yellow light from ,l

above and developed purple, then the upper layer is exposed to blue light and developed yellow. The exposure of the middle layer 2 to green light from below, or to blue light from below in the case oi' a yellow filter layer 4 between the top two layers, can, be less satisfactorily accomplished by exposing in either case after preliminary reduction of the green blue dye formed in the lower layer 3 to its easily re-oxidized insoluble leucoforms. Reduction -of the residual silver halide of the upper layer I maybe eifected here, as in similar cases, by alkaline solution of the leuca-forms of various yellow vat dyes, best under exclusion of atmospheric oxygen to prevent fog. Oxidation stability of the "'red sensitizer, which may here be also sensitive to yellow, is no more required, which represents a very great advantage compared to the method of execution previously described. because the choice of proper red sensitizers is much less limited,A and many may be used which excel by complete insolubility or inability to Under certain circumstances, even oxidation-stability of the sensitizer of the middle layer is unnecessary, as proven by the following examples:

'I'he residual silver halide of the middle layer 2 can be exposed also to blue light ,through the support S, if suilicient blue sensitivity of the upper layer I was obtained by high sensitization which is then lost during conversion by oxidation of the primarily reduced silver, since here the undesirable eect of the very little sensitive upper layer is not feared. The hardly noticeable different conditioned by the lower blue (or purple) image can be corrected by creating a blue (or purple) indo-phenol or azo-methine dye in ment which, however, in contrast to theilnalY image dye ofthe lower layer (indigo, Russigs split by acid.

addition to the silver in theiirst general develop: u

After making the residua silver-,hande of the middle layer 2 developable with blue light through this lower layer now uniformly colored, the intermediate dye of the lower layer is destroyed. This may also be done after completion of the three-color' image, if also the iinal yliw dye of the upper part image is 'stable to a i As a further example, the middle layer 2 is exposed to yellow light from either side and developed purple, then the upper layer I is exposed to blue light and developed yellow, iinally the lower layer 2 to blue, white or red light and developed green-blue after removal orl conversion of the primarily reduced silver, if there is a yellow filter layer 4 betweenthe middle and upper layer or if the latter is colored yellow and the yellowgreen sensitizer alone is oxidation-stable. The lower layer 2' can also flrstbe exposed to red light and developed green-blue, then the upper layer I to blue light and developed yellow, or in reverse order; after short action of potassium ferricyanide or suitable` solvents on the newly reduced, highly dispersed vsilver of the upper layer, the middle layer 2 is made developable with yellow light and developed to the purple part image. It would be less correct to expose to red light the residual silver halide of the lower or to dissolve it, and finally to expose the middle i layer 2 to yellow and to develop purple.

The stability of the green-yellow sensitlzer to oxidation is not absolutely necessary for the middle layer 2, if at least the yellow illter layer I which also absorbs ultra-violet, or yellow coloring of the upper layer is present, so that in the triple layer, according to the present invention, one can entirely dispense with oxidation-stable sensitizers and pay more attention to prevention of diffusion of sensitizers from one layer to the other. The lower layer 3 is exposed to red light after general black development and is developed green-blue and treated further according to one of the following methods:

It would be simplest to expose the middle layer.

to ultra-violet light through the lower uniformly blackened layer and through the green-blue dye not absorbing ultra-violet or to infrared light. if it was also sensitized for this in addition to green-yellow, and to develop purple. This requires long exposure, however, since the lower layer absorbs most of the light. Even in exposure of the upper layer to blue light, because the primarily reduced silver prevents a complete exposure through the depth of the upper layer, some residual silver halide will be left and de, veloped in the color of the middle layer, if this is developed later.. By the use of ultra-violet light for exposure of the residual silver halide of the upper layer this evil is eliminated, according to the invention. The same effect is gained with soft X-rays, if the upper part image is produced last.

It is, however, better iirst to expose the upper layer to ultra-violet light and develop a yellow image. Alternatively it may be treated brieily with a l to 2% solution of potassium" Ierricyanide or with a silver solvent converting or dissolving only the highly dispersed silver ot the upper layer entirely or partially into white silver ferrocyanide, without allowing this to take place in the other two layers. The residual silver halide of the upper layer is then converted into a yellow image. The lowest layer is then exposed to red light and developed to blue-green. If two lter layers 4 and 5 are provided a yellow and a red or orange one, or two yellow layers, exposure of the residual silver halide of the lower layer can lbe done even with blue light. The middle purple part image is then obtained by oneof the following methods:

(a) The residual silver halideof the middle layer is made developable by pre-treatment with about 0.02% solution of thiourea, thiosinamine etc., or analogously-acting sulfur derivatives, or with a 0.001% solution of zinc chloride, by means of arsenite, hypophosphite, thallo salt, triamido phenol, masking dyes, especially in the presence of heavy metal salts or other suitable agents, which may also be added to the correspending color developers; it -is then developed purple, and finally all silver removed 0r Xed out. The pre-treatment may be omitted, if a color developer is chosen which acts so vigorously onraddition of ammonia or alkali, or also alcohol and acetone, preferably without air, that the residual silver halide of the middle layer is reduced without exposure after prolonged `is very transparent to ultra-violet light.

aeeiei treatment. This is especially true for a silver chloride emulsion layer which, unexposed, is suftlciently stable to the color developers containing soda which is necessary for the two outer layers. The residual silver bromide of the middle layer is, however, reduced without pre-treatment or exposure by most leuco-vat dyes in alkaline solution or one containing alcoholror acetone with precipitation of the dye on the image. Residues of the latent images in the other two layers can be destroyed previously by the action of mild oxidizing agents, as potassium ferricyanide and ammonia etc.

(b) All previously reduced silver is removed entirely or for the largest part, combining with it possibly the destruction of lter dyes by oxidation or acid, or converting into ferrocyanide etc., exposing the residual silver. halide of the middle layer from both sides to white, or better,`

ultra-violet light or to soft X-rays and developing purple, and ilnally. removing the silver and ilxing out, if necessary, both of which are possible with Earmers reducer. The residual silver bromide can also be reduced to black silver with vigorous ordinary developer or with any organic or inorganic reducing agent; this is then converted into very easily oxidizable highly dis- .l

lpersed silver chloride by bichloride of mercury withthe color developers even without exposure.

(c) The residual silver halide of the middle layer is at once made developable by exposure from above or from both sides to ultra-violet light or better soft X-rays, and the corresponding part image is developed. This is possible, because very tine-grain and not cohering reduced silver silver is then removed.

(d) The residual silver bromide of the middle layer is converted into silver iodide or one of its complex salts, if necessary, after removal of the metallic silver, and this is colored purple or green-blue by mordanting dyes. The metallic silver is removed now or earlier land fixed, if necessary. The dyes are made insoluble before removal of the mordanting-agent by proper precipitants, phosphotungstate etc. If the middle layer consists of silver chloride, its residue can be converted into silver ferrocyanide,.and further into red nickel-dimethylglyoxime or into yellow titanium ferrocyanide which latter yields a green-blue image with blue basic dyes. The silver ferrocyanide originating from the silver chloride, can also be converted into other suitable non-tanning mordanting bodies which are colored purple or green-blue by basic dyes and maybe removed after insolubilization of the dyes in order to attain greater transparency.

Since silver bromide must withstand four developments, three of them with color developers containing sulte-free sodium carbonate or a1- kali, in order to obtain vigorous part images, fog is diilicult to avoid. It is, therefore, recommended to use an upper or middle silver chloride layer, especially with film coated on both sides,l where the -film itself or a coated filter layer can contain colorless substances absorbing ultraviolet and the red-sensitive silver halide layer is alone on one side, because silver chloride is colored, even if it is not exposed,-and still more so unexposed silver bromide. Colored development o! the original residual silver chloride can be even entirely dispensed with, since it is easily converted into silver ferrocyanide and this into colored substances, or easily colored mordanting bodies. One is not dependent upon the easy re- Thel which can also be eiiected by addition of potassium bromide, etc. to the last color developer. The residual silver ferrocyanide could also be reduced with a vigorous color developer directly, or with formation of the color image from silver iodide which is readily obtained from the residual silver chloride.

It is possible to utilize the diil'erential development properties of silver chloride and bromide to forman image in the silver chloride only. Since silver chloride 'develops more rapidly than silver bromide, a strongly diierential action is obtained particularly when the chloride layer is uppermost. In this case development is ordinarily not carried to completion but is stopped when a usable, even ii incompletely developed image, is obtained prior to any substantial development oi' an image in the layer containing silver bromide. In such cases other expedients found useful in diil'erential development may also be employed such as the use of retardants or hardening the lower layer.

The later undesired further development oi the exposed but undeveloped residue may be avoided by converting the chloride to another salt.

The silver chloride layer only may be developed to a black silver image followed immediately with development oi' the residual silver chloride with a weak color developer which does not rapidly attack the exposed silver bromide. The residual silver chloride may also be directly or indirectly converted into a colored substance or a mordanting body, as described in detail later. Only then, the two silver bromide layers are simultaneously developed in an ordinary developer, `and ilnally, the residual silver halideoi the same developed in succession to the correpart images, even when no filter layer or only one ispresent and sensitization is not even stable to an ordinary black developer. Several such processes will be outlined. (a) The latent image of the middle silver chloride layer is first developed alone with a weak ordinary developer, and

then, with a color developer which is `only strong enough to reduce the residual unexposed silver chloride, but not the exposed or unexposed silver bromide, the middle part image is developed. For this purpose, the silver chloride of this layer could be pretreated with solutions of very mild reducing agents or compounds containing sulfur which make the residual silver chloride oi' the middle layer developable, but not the unexposed vsilver bromide. Since the middle-layer is entirely blackened by metallic silver, the two other layers can be independently exposed to blue .light after ordinary development, and their residual silver bromide can be individually developed in color.

(b) Furthermore, the residual silver chloride of the middle layer can be converted into silver i'errocyanide alter usual black development, the latent images oi the other two layers developed in an ordinary developer, the silverferrocyanide ot the middle layer reconverted into silver chloride and this silver chloride and the residual silver bromide oi one or both layers made developable by exposure chemical pre-treatment or in any other manner. Now the middle color image is developed with a speciiic silver chloride developer and the residual silver bromide transformed into the inert state by mild oxidizing agents, as for the destruction of chemical fog, then, by a bath of sulte, bisulte, hydrazine or hydroxylaminesalt it is made suiiiciently light-sensitive and each silver bromide layer individually ,exposed and developed in color. The silver ierrocyanide obtained from the residual silver chloride is initself sufliciently dense to allow the residual, highly sensitive silver bromide of the lower layer to be given a short exposure; a better procedure is to convertl with lead chloride or thorium salt into' the corresponding ferrocyanides and to convert the newly obtained silver chloride into silver ferrocyanide. All silver ferrocyanide couldaiso be converted into lead chromate which acts like a yellow iilter in the individual exposures of the two outer silver bromide layers and is removed at the end. All this holds especially true, if the very tine-grain silver bromide of the upper layer has lost its high sensitivity which it had acquired through high sensitization. 'I'he silver ferrocyanide of the middle layeror the` zinc ferrocyanide obtained from it with zinc chloride or zinc bromide may serve as an excellent mordanting substance for coloring with yellow basic dyes, resulting in a middle yellow-black lter. The two latent silver bromide images can now be developed under certain conditions, unless this has been done before, and the residual silver bromide of each layer individually exposed vand i developed in color.

(c) Ai'ter simultaneous development of all three latent imagesfthe residual silver chloride of the middle layer is converted 'into silver ferrocyanide and this into yellow titanium ferrocyanide or intoany other non-tanning colored insoluble ierrocyanide, or also through nickel ferrocyanide y into nickel-dimethylglycoxime or other insoluble colored and easily split complex compounds which act as middle light filters in the exposure of the residual silver bromide of the two outer layers. The insoluble ferrocyanides are split by sodium carbonate or alkali, the complex salts mostly by acids. -The silver chloride formed can be reconverted into silver ferrocyanide which is practically insensitive to light, or it is converted withbromine salts, since silver bromide formed in this way is only very slightly sensitive to light in comparison with the silver bromide of the lower layer. After colored development of the two outer layers, silver halide may be regenerated from the silver ierrocyanide of the middle layer and this made developableby thiourea, stannous salt, masking dyes etc. or byintensive exposure to ultra-violet or X-rays, and developed in color or converted,V

similar to the original silver ferrocyanide, with a vigorous color developer directly into vthepart color image. ierrocyanides are removed and the lter dyes washed out. v

(d) All three layers can be developed simultaneously and the residual silver chloride. converted into silver ierrocyanide and this reconverted into silver chloride which becomes very Finally, all silver and the insoluble silver halide of all three layers can be, made developable simultaneously by ultra-violet or X-rays, by pre-treatment with thiourea etc., and the silver chloride of the middle layer developed in color, so that a homogeneous color filter is created in the middle. The latent developing ability of the residual silver bromide is now destroyed by the action of mild oxidizing reagents, p-phenylenediamine and acid etc., suillcient general sensitivity created by a bath of sulte, bisulilte, hydrazine salt, hydroxylamine etc. or by optical sensitizers in preferably weak ammoniacal solution, and the two outer emulsions individually exposed and developed in color. If the middle emulsion is still sufiiciently yellow-green or redsensitive after ordinary development of the silver chloride, it is exposed to the proper light and the residual silver chloride developed in color, so

that a homogeneous silver filter also results. The latent images are then developed in the two outer silver bromide emulsions, and finally, their residual silver bromide individually exposed and developed to the corresponding part color images. The same holds true, if the sensitizers mentioned do not survive the rst general development, but if the middle emulsion contains in addition a resistant infraredsensitizer, so that the residual silver. chloride of the middle emulsion can be made developable by infrared rays for which the two outer silver bromide emulsions are absolutely insensitive and which is not harmful to the latent images contained in them. Since a yellow lter between the upper and middle emulsions is indispensable for nature photography, all reduced silver can be removed after general black development of all three emulsions, and then the middle and lower emulsions simultaneously exposed yto blue light, first the residual silver chloride, and then the residual silver bromide developed in color, and finally, the part color image developed in the upper silver bromide emulsion; or viceversa; The silver is removed at the end.

(e) If an upper or middle silver chloride emul-A sion exists it is possible to convert the residual silver chloride into silver ferrocyanide, and only then proceed to general black development of the two `silver bromide emulsions. Without preliminary removal of the metallic silver bromide, the lower (or in reverse order for exposure through the back: of the upper) red-sensitive emulsion is exposed to red rays (if a green-sensitive emulsion to green rays) and developed in the approximately complementary color. The residual silver bromide of the middle emulsion is then made developable with thiocarbamide etc. and the corresponding part color image developed.

Finally, the silver ferrocyanide of the blue-sensidyes. A great advantage here is that the sensif tizer for the emulsion which is most remote during exposure does not have to be oxidation-stable. An infrared sensitizer which is stable to the developer and mild oxidizing agents can also be added to this emulsion or to the silver chloride emulsion. The residual silver halide of this emulsion. can be made developable through infrared light, even if the original sensitizer has become ineiective. Any other sensitizer could, however, be added to the lower emulsion in addition to that for red, for which the middle emulsion is insensitive. An infrared sensitizer which is stable to the developer, can generally be added to the lower emulsion in addition to the red sensitizer. After general primary development, the residual silver bromide of this emulsion is iirst exposed to infrared rays and developed in color, the other two emulsions can then be made developable with thiourea etc., and iirst the silver chloride, then the silver bromide emulsion developed in color. In printing, the lower emulsion can be sensitized exclusively for infrared, the middle for red, orange, yellow or'green, and the residual silver halide made developable with this light.

'Ihe use of silver chloride is especially advantageous with lms coated on both sides of the types shown in Fig. 5, on one side with an outer blue-sensitive silver chloride emulsion 25 and an inner silver bromide emulson 26 sensitized for green-yellow or red-orange on one side and with a silver bromide emulsion 21 sensitive to red or yellow-green on the other side. After general black development and perhaps removal or conversion of the reduced silver and also repeated exposure of all residual silver halide, each side is developed independently from the other. First, l

the residual silver chloride of the double-emulsion-coated side is developed in color, then the silver bromidel of the middle emulsion or middle zone below, finally the silver bromide emulsion on the other side, or vice-versa, followed by removal of all reduced silver. Instead of a second exposure, it may also be pretreated with thiourea stannous salt, masking dyes. etc., or the reduced silver is removed entirely or for the greatest part and both sides exposedto ultraviolet rays.

If the red-sensitive emulsion `21B is in the middle, as in Fig. 6 with color filters 4 and 5 on one or both sides, if desired, the previous developing procedures can be applied here, if they are correspondingly changed. The following examples may serve as an example: If no filters are present, the middle emulsion is exposed to red light after removal or conversion of the primarily reduced silver and developed green-blue, the lower 26B to yellow and the upper 25B to blue light, etc. The lower emulsion can also be exposed to yellow light directly after black development and developed purple, then all silver converted into silver ferrocyanide or removed. This is followed by exposure of the middle emulsion to blue and development of the yellow part image. In the event of an upper yellow illter, the upper emulsion can be made developable immediately after black development in order to obtain the yellow .part image; the middle emulsion is then made developable by thiourea etc. or after removal or conversion of all reduced silver by exposure totwhite light from both sides. If yellow illters 4 and 5 or ultra-violet-absorbing iilter layers are arranged on both sides of the middle emulsion, the two outer emulsions are made developable with blue or ultra-violet light, and the middle emulsion in the manner just described. If ythe -silver chloride emulsion is on top, one can expose to yellow light from 4the back, after general development, and .the

5 lower purple image can be produced. The upper and middle emulsions are then made developable directly by thiourea, etc., or, after preliminary removal or conversion of the reduced silver of at least this emulsion, by exposure to white or blue light from above. The yellow part image is then produced in the upper emulsion with a color developer whichacts only on silver chloride, then the green-blue part image in the middle emulsion with a vigorous developer.

In films coated on both sides, all previous and subsequent methods of three-color-reversal development and redevelopment, as well as the primary .three-color development and combination processes can be made much simpler, as can. be seen from following examples. According to the invention, the most favorable results are obtained, when the blue-sensitive and the middle emulsions are on the same side of the lm and the redor yellow-green-sensitive one on the rear surface, as in Figs. 5, 6 and 7, because one-sided color-development can be accomplished by many perfected methods without changing the latentimage or the residual silver halide of the other side. For nature photography, triple-layer illms can be used, coated on the side not carrying the silver chloride emulsion 25C, with a layer 6C which at first retards development, as alcohol-soluble lacquer, benzyl ether cellulose, a stearine layer soluble in the alkaline color developer etc., in order to be able to accomplish one-sided development with greater certainty. After completion` of the part color image orvimages on one side, the temporary coating is removed and the colored development of the other side completed. Since the doubleemulsion side contains the yellow iilter 4 between the two emulsions 25C and 21C. the residual silver halide of the blue-sensitive emulsion can be made developable with blue light after general black development and developed to the yellow part image then both other emulsions are made developable with thiourea, etc., and one after the other developed independently in colors. If the double-layer consists of a silver chloride and silver bromide emulsion asin Figs. 6 and 7, the residual silver halide of all three layers can be I made developable by this pre-treatment. The silver and chloride emulsion alone is rst developed in color, then the two other silver bromide emulsions independent of each other. The procedure is analogous in the two-zone double-layer, if the emulsion which is not sensitized by zones is alone on one side of the lm. After general development, the outer zone of the other emulsion is exposed to blue light, developed in color, then 00 the zone underneath made developable with thiourea etc., and the next part color image dcveloped in it; or the residual silver halide of the emulsion adjacent to the support is immediately developed in color with a vigorous developer, then the other side developed in color.

Specific action of a developer on silver chloride does not depend on its chemical constitution -alone, but even more on the working conditions. P-aminophenol, p-dichloraminophenol,A p-aminodimethylaniline develop silver chloride even as free bases or their salts in the presence of bicarbonate amidol and diaminoresorcln can be weakly acidied without losing their developing 'power for silver chloride. Pyrogalloldimethylether in Aiti alkaline solution works much more rapidly on silver chloride than on silver bromide and yields also much stronger brown-red images after removal of the s ilver with Farmers solution, pchlor-o-aminovic.m.xylenol in aqueous sodium carbonate solution yields 'strong lemon-yellow im- 5 ages with silver chloride emulsions, while silver bromide even in alkaline solution develops much slower to very much weaker color images. Often the developing power is inten'sied by the' presence of a coupling component or this power is l0 even created by it: p-amlnophenol and dichlor-paminophenol do not develop the latent image on silver bromide gelatine emulsions, but do develop in a solution with m-toluylenediamine, which in itself is, of course, no developer. When using its 15 salts in the presence of bicarbonate, a blue dye image is formed which is only slightly waterstable. Even p-amino-dimethylaniline plus bicarbonate does not develop silver bromide. In the presence of 3nitro-phenylmethylpyrazolone, however, a brick-red image is slowly produced.

-but much more quickly on silver chloride gelatine emulsion.4 Also coupling developers containing sodium carbonate can act selectively to a certain 25 degree: p-aminodimethylaniline and phenyl-J- acid Ciba yield very strong blue-green images in sodium carbonate solution on silver chloride emulsion, much weaker images on silver'bromide emulsions. v Similar differences exist in coupling 30 with carbonyl-J-acid, forming dark grass-green images. 7-amino--naphthol couples in alkaline solution `with 'p-aminodimethylaniline to a darkgreen dye; but the images are intense only on silver chloride emulsion, while silver bromide, 35 under the same conditions, yields only very weak dye images. The addition of NaCl or KBr also ailects the selectivity. If one is not absolutely dependent on developer solutions prepared with alkali, if the developer and the possible coupling 40- component are also soluble in water, or as most of the acid methylene compounds, in very weak alkalies (bicarbonate, borax, secondary sodium phosphate, ammonium carbonate, sodium glycocoll etc.) one is at liberty to make the simple and 45 coupling color developers mentioned above specic for silver chloride by section and quantity of alkali. As the examples show, the working conditions can be' changed in many ways for this purpose, so that it is unnecessary to give general 60 rules. It must be decided rather in each individual case by the nature of the experiment, with which .weak alkali,- with which component or with which concentration and duration of the developer the best selectivity for silver chloride can 55 v be obtained.

Three-color direct development 4veloperand oxidation-stable sensitizers are not absolutely required. In addition to this, they make immediate development in the correspond- 70 ing color of each part image possible-after exposure and without previous general black development. Unfortunately, the primary threecolor development yields only a complementarycolored negative which in turn yields a correctly colored positive only by printing in the same manner or by exposure-printing methods.

In three-color direct development, one can use only one single tanned layer or one protected by intermediate layers. This will usually be the red-sensitive silver bromide gelatine'layer 3 adjacent to the support which may be so strongly tanned that it is not developed in the general black development, nor in the individual color development oi the two other layers, but only after removal of the tanning. The upper layer consists of silver chloride or highly dispersed silver bromide, the middle layer of fine-grain or also coarse-grain silver bromide sensitized for green-yellow; strongly swelling gelatine is used ifor both. The silver chloride or highly dispersed silver bromide emulsion is developed first, thenl the middle silver bromide layer is developed in a more vigorous developer to the corresponding part color image, or these two layers are xed alone, since thiosulfate cannot penetrate the lower tanned emulsion; on moderate duration of the iixing actio the last part image is now developed with a stronger alkaline color developer, if necessary, after preliminary detanning or removal of the retarding action of a illter layer between middle and lower emulsions.

A very tine-grain silver chloride gelatine emulsion or collodion emulsion can be tlrst coated on the lm, above it a silverbromide-gelatine emulsion sensitized for green-yellow. Both or the middle layer are thoroughly hardened by formalin or better by the more recent tanning agents without after-action described in U. S. Patents 1,870,354 and 1,941,852, or only in zones as in German Patent 486,644. One can also coat an emulsion ,of silver chloride collodion sensitized in the same manner and above this the tanned silver bromide gelatine emulsion; or both lower layers consist of collodlon, or also the silver halide is emulsiiled in another nonswelling colloid.

as cellulose acetate, ethyl cellulose etc. Th'is is covered by a soft red-sensitiveilver bromide gelatine emulsion. The silver chloride emulsion can also be arranged in the middle. The normally compounded green-blue developer will only develop the untanned red-sensitive emulsion during the usual time o! action. By prolonged action of a color developer acting only on silver chloride, the corresponding part im'age is ob- .tained, and the corresponding part color image is developed from the silver bromide of thelow- Aer emulsion with a vigorous, perhaps ammoniacal color developer or one containing fixed alkali; the silver is nally removed with Farmers reducer. Tanning of the emulsion can be entirely or partially removed before development by alkalies, oxalates, etc., and suitable substances may be added for this purpose to the color developer.

The individual emulsions can also be separated by intermediate layers impermeable to the developer, especially the upper one from the two others. These layers can consist of gelatine, collodlon, cellulose acetate or any' other suitable colloid, in -order to make possible the independent direct colored or reversal colored development. After completion o! the upper part color Y' image, the tanning o! the gelatine is removed or the collodion etc. made permeable to aqueous solutions by alcohol, acetone etc. followed by development of the colored part images in the two lower layers according to previous methods; this is especially simple, if one of the two layers consists of silver chloride. The intermediate layers layer a conversion product is obtained from the highly dispersed reduced silver; this is colored developed or used for mordanting after further conversion into copper ferrocyanide or zinc ferrocyanide etc. The silver halide formed from the more coarse-grained negative silver of the middle layer is obtained by prolonged action of potassium ferrocyanide and potassium bromide or sodium chloride is then developed in color, al-4 sol the one formed on the other side of the film. All three emulsions can also -be situated on the same side of the lm, if a iter layer is inserted between the two coarse-grain emulsions; or two highly dispersed silver bromide emulsions with a yellow filter between them on the lower coarsegrain emulsion. After development and ilxing. the metallic silver of all three emulsions is converted into silver ferrocyanide by prolonged action of potassium ferricyanide, and the two upper emulsions containing highly dispersed silver ferrocyanide are converted into a similar silver halide'by short bathing in potassium bromide or sodium chloride, lead chloride solutions etc. The upper layer is then exposed to blue light and developed in color, then the middle layer from the back and developed to the corresponding part color image; the lower emulsion is ilnally developed immediately with a vigorous color developer after intense exposure of the silver ferrocyanide; or it is ilrst converted into silveloped in' color, iinally the upper layer exposedv to blue light from above and developed in color. Reversely, one could also make ilrst the upper layer developable with blue light and develop in color, then expose the twoy others through the back to blue light and treat further as above. No color sensitivity of the middle layer is required. A blue-sen'sitive silver chloride emulsion could be coated at the bottom, a highly dispersed yellow-green-sensitive silver bromide emulsion in the middle, and a coarse-grain redsensitive emulsion at the top, all untanned. After exposurefthe silver chloride is converted into silver ferrocyanide by potassium ferrocyanide without attacking the latent images; then the highly dispersed silver bromide is developed in color, followed by the coarse-grain silver bromide. Finally, the silver ferrocyanide is reconverted into silver chloride' or silver bromide and this developed in color. The latent developable state is not lost during these operations. The silver is then removed with Farmers reducer. If the emulsions are coated in reverse order and also the blue-sensitized silver chloride emulsion is highly dispersed, this can be developed directly after exposure with a very weak color developer. The highly dispersed silver bromide of the middle emulsion is now developed in colorI with aA stronger developer and then the, coarse-grain silver bromide with a color developer of normal composition. All `three emulsions could also be rst developed as usual, the residual silver chloride then converted into silver ferrocyanide, then the residual highly dispersed silver bromide-developedin color and finally the coarse-grain silver bromide.A The last part color image is obtained after reconversion of the silver ferrocyanide-into silver halide or directly with a vigorous color developer. Then the silver is removed. This is also satisfactory for three silver bromide emulsions, if .the lower coarse-grain emulsion alone is tanned; the middle emulsion can then contain coarser silver bromide and theA upper one highly dispersed silver bromide. In director reversal color development, the (residual) highly dispersed silver bromide is.first developed in color, then the [middle emulsion and, nally, the lower tanned emulsion. The silver is then removed. l

If an upper silver chloride and a middle silver bromide emulsion is on one side of the lm, the last silver Abromide layer on the other side; only the silver chloride emulsion is rst developed after exposure with a proper weak color developer. The residual silver chloride is converted into silver bromide or silver ferrocyanide which can also be effected by correspon-ding additions to the color developer; then the silver bromide layer, and independently the emulsions of the other side, are developed to the corresponding part color images, followed by removal of the silver in Farmers solution. A yellow lter is inserted between the upper and middle emulsionsA the middle layer is sensitive for yellow-green, the lower for red alone. The middle layer adjacent to the support consists of silver chloride gelatine emulsion or collodion emulsion.

On one side of the lm, a middle hardened4 silver bromide gelatine or collodion emulsion may be coated and above it a non-hardened gelatine emulsion containing highly dispersed silver bromide. Often it is even suiicient to'aaoat a gelatine emulsion containing highly dispersed silver bromide on. a non-hardened normal negative emulsion. The upper `and lower layers are individually developed, most of the silver halide fixed out and the middle tanned -layer developed for a longer time into the corresponding'color, pos- `sibly after detanning, and nally, the silver isrremoved. Such a triple layer could, of course,

also be used for three-color reversal development. I

The emulsion situated alone ono'ne side of the lm can,l according lto the invention, consist o f. a red-sensitive collodion' emulsion. If the middle layer on the other side consists of the same emulsion, the thickness of the cellulose acetate film and with it refraction can be considerably reduced. Part of the gelatine of the blue-sensitive emulsion can be substituted by colloids which are less inclined to swelling. f Substances opposing swelling may also be added to the developing solutions, or one may moderately tan before development.

development and in direct three-color develop-y ment, the silver halide contained in the layers serves for color development, either that containing the -latent image or that remaining after .usual black development. Another possibility is at any stage after removal of the primarily formed silver and to reconvert the metallic silver into silver chloride or silver bromide. In all these cases, the advantage is oiered that the regenerated silver halide cany vbe obtained in highly dispersed form, especially as a pseudomorpho after formation of intermediate silver lferrocyanide or during treatment of the metallic silver with bichloride of mercury or copper chloride, also with a mixture of both orof copper vitriol with potassium bromide. Any oxidizing agents are suitable for hehalogenation in the presence of potassium bromide or sodium chloride, as long as they do not tan. The silver chloride formed in this manner is very easily reduced, so that the 'color developers applicabley in this case do not requir'ev any or only very weakalkali, or also the reduction takes place without exposure with Iformation of the colored image.

This is especially important for the middle part image. If `one has converted into silver chloride, two partv images can be produced by colored development, the third, or middle layer, which is usually diilcultly 'accessible to exposure is developed by toning or mordanting processes,

by conversion of the silver chloride of this emu1.

sion into silver ferrocyanide or better into the corresponding mordanting bodies and coloring, or directly into color substances, as colored ferrocyanide or red nickel dimethylglyox'ime or compounds mentioned later.

If properly compounded color developers are used acting differentially on silver chloride, one can, after general black development, convert -directly into silver chloride or through silver other ferrocyanide without preliminary fixing out of I the silver bromide. Fixing takes place only at the, end with Farmers reducer. The color substances of the middle emulsion obtained by different methods than colored development must, of course; also be stable to potassium ferriand ferro-'cyanide or thiosulfate. It would be less advisable to convert the. unused silver bromide into. silver iodide which is also'hard to reduce, and then to rehalogenate.

If lboth upper layers consist of sensitized silver chloride, the middle silver chloride layer can be developed in color with a developer acting only on silver chloride, after superficial colored development by controlled diiusion of the outer silver chloride layer; then the lower silver bromide layer can be independently developed.

In certain processes, the intermediate gelatine layers .are relied on, in part, to prevent diffusion.

The superficial eiect on the upper layer created by this can be attained much more perfectly, if first the middle layer is treated so that it is excluded, 'and then forms, together with the two intermediate filter layers, a neutral zone of approximately triple thickness. After this inactivation of the middlev silver halide layer,indi

'vidual color development of the upper-layer can then be accomplished by controlled diffusion of so many kinds that in the following only the most important ones can be explained:

In reversal development, the primarily reduced silver of all three silver bromide layers can be tanning developer yielding a black image in each,

removed or at least converted into silver ferrocyanide witli potassium ferricyanide. Then the residual silver bromide of the middle 'layer can be exposed to yellow or red light and developed in color, provided that its color sensitivity has not been destroyed by developer and potassium ferricyanide. The residual silver bromide of the two other layers is now made developable with thiourea, stannous salt etc., or by re-exposure, and the upper part image is obtained by supercial action of ,a color developer by known methods of controlled diffusion, then in the usual manner the lower part image.

Similar results can be obtained with a triple layer having a silver bromide gelatine emulsion only'in the middle; above and below, however, silver chlon'de emulsions, preferably with pure or colored or ultra-violet absorbing intermediate gelatine layers. Other colloids less permeable to water than gelatine can be used for the latter and also for the middle silver bromide layer. The middle silver bromide layer is especially desirable in two ways, as the following examples show: y

The three layers are rst submitted to 'a nonand this is bleached out in the usual way. Then, after selective exposure of the middle layer to light to which it is ydifferentially lsensitive, and development of this' layer to an appropriate color,

a color developer acting specifically on. silver' chloride is allowed to penetrate superiicially, of course, deep enough to develop completely the latent color image of the upper layer. An effect on the lower silver chloride emulsion is eliminated with certainty, since the surface developer to reach the lowest layer has to penetrate two gelatine intermediate layers, in addition to the mid- 40 dle silver bromide emulsion layer. The lower part color image is thendeveloped by prolonged action of another color developer specific for silver chloride.

Another method is to allow a properly com- 45 pounded solution of potassium ferro-cyanide to diffuse differentially and superilcially after general ordinary development` This converts only'v the silver chloride ofthe-upper layer into silver ferrocyanide, but certainly does not act on the 5o'residual silver chloride of the lower emulsion which latter is then directly developed in color. After reconversion of the silver ferrocyanide of the upper layer into silver chloride, this is reduced with a specific color developer, thenv the re- 15.', sidual silver bromide of the middle layer after making it developable by thiourea eta., It is less desirable to develop the residual silver broniide of the middle layer first in color after correspond- Jing pre-treatment and only to then reduce the no silver ferrocyanide of the upper layer after conversion into silver chloride or directly with a vigorous color developer. The silver ferrocyanide of the upper layer could be converted into the l corresponding part color image either directly or i after colored development of one of the two other part image,y also by conversion into a colored ferrocyanide, etc., or into a mordanting body.

I consider all of the embodiments of nlm and processes for treating them disclosed herein, and

.whether specically claimed or not, generically and specifically a part of my invention and I desire to secure by Letters Patent of the United States'protection on all the novel subject matter Aherein disclosed.

Having thus described my invention, what I claim as new and desire to be secured by Letters Patent is:

1. A photographic element for use in color 'i photography comprising a support having upon one surface thereof at least two superposed emulsion layers differentially sensitized for diiferent colors, at least one oi which layers is of silver chloride emulsion and at least one of which is of silver bromide emulsion, the silver chloride layer being of very fine grain and outermost, and the silver bromide layer being of coarse grainl and beneath the silver chloride layer.

2. A a photographic element for use in color photography comprising a support having upon one surface thereof at least two superposed emulsion layers differentially sensitized for different colors, at least one of which layers is of silver chloride emulsion and at least one of which is of silver bromide emulsion, the silver chloride layer being above the silver bromide layer, and the silver bromide layer being less` pervious to water than the silver chloride layer.

3. A photographic element for use in color photography comprising a support having upon one surface thereof at least two superposed emulsion layers differentially sensitized for different colors, at least one of which layers is of silver chloride emulsion and at least one of which is of silver bromide emulsion, the silver chloride layer4 being of very ilne grain and outermost, and the silver bromide layer being of.coarse grain and beneath the silver chloride layer, andless pervious to water than the silver chloride layer.

4. A photographic element for use in color photography comprising asupport having upon one surface thereof at least two superposed emulsion layers diilerentially sensitized for different I colors. at least 'one of which layers is of silver chloride emulsion and at least one of which is of silver bromide emulsion, the silver chloride layer being of very ne grain and the silver bromide' layer being of coarse grain, the speed of the several layers being of the same order.

5. A photographic element for use in color photography comprising a support having upon onesurface thereof at lea'st two superposed emulsion layers differentially sensitized ior`A diierent colors, at least one of which layers is of silver.

chloride emulsion and at least one of which is of silver bromide emulsion, the silver chloride layer being above the silver bromide layer, and thesilver bromide layer being less pervious to water 'than the silver chloride layer, the speed of the several layers beingof the same order.

- KARL SCHINZEL. 

